This invention relates to radars used to detect and track targets in clutter backgrounds and in particular to a wide bandwidth radar of that type having improved signal to clutter response characteristics.
A need exists to extend the present capability of guided weapons to include all-weather air strike operations against tactical targets. Microwave radiometric guidance techniques provide the potential to strike targets partially obscured by foliage, clouds, or adverse weather. Trackers utilizing these techniques are capable of operating in both active and passive modes.
Past work has shown that passive microwave radiometer techniques can be used to detect and track metal targets in foliage backgrounds even when partially obscured by weather, foliage and camouflage. However, for most tactical warfare applications, detection range is not sufficient and false targets such as pools of water and background variations are a significant problem.
With regard to active mode operation, a class of frequency-agile radar has evolved which uses pulse-to-pulse frequency change to smooth clutter fluctuations. Typically, using spin-tuned magnetrons, these radars achieve detection ranges of greater than 10 miles against targets in sea and terrain backgrounds. In this class of radar the frequency of the transmitted pulse is changed from pulse to pulse and a narrowband receiver is programmed to follow the frequency variation. The primary problem with this approach is the complexity/cost of the frequency agile transmitter and receiver.
A second active mode approach is to use an FM-CW radar with wide frequency deviation. With this approach, range gating is difficult because sweep linearity must be obtained over a very large frequency range. Also, since it is a CW system, feedthrough of transmitter noise sidebands into the receiver limits system performance.
The present invention relates to active mode operation and specifically to a class of active radars using wide bandwidth to suppress clutter fluctuations from terrain and sea backgrounds and to suppress signal fluctuations and angular glint from complex targets such as tanks. Thus signal-to-clutter ratios are increased such that search, acquisition and guidance can be accomplished for small targets such as tanks in terrain background and small ship/boats at sea.
Compared to the magnetrons used in frequency-agile systems, the solid state transmitter power is very low. However, since radar range has a 4th root dependence on power, ranges usable in missile terminal guidance systems are achievable. The major advantage of the pulsed, wide bandwidth radar over the FM-CW radar approach is the ability to use time gating to discriminate against rain backscatter, system thermal noise, and false or multiple targets.